THERMAL-CONDUCTIVITY OF WATER-SATURATED ROCKS FROM THE KTB PILOT HOLEAT TEMPERATURES OF 25 TO 300-DEGREES-C

The conductivitites of selected gneiss (two) and amphibolite (one) cor e samples have been measured under conditions of elevated temperature and pressure with a needle-probe. Water-saturated thermal conductivity measurements spanning temperatures from 25 to 300 degrees C and hydro static pressures of 0.1 and 34 MPa confirm the general decrease in con ductivity with increasing temperature but deviate significantly from r esults reported from measurements on dry samples over the same tempera ture range. The thermal conductivity of water-saturated amphibolite de creases with temperature at a rate approximately 40% less than the rat e for dry amphibolite, and the conductivity of water-saturated gneiss decreases at a rate approximately 20% less than the rate for dry gneis s. The available evidence points to thermal cracking as the primary ca use of the more rapid decrease in dry thermal conductivity with temper ature. The effects of thermal cracking were also observed in the water -saturated samples but resulted in a net decrease in room-temperature conductivity of less than 3%. These results highlight the importance o f duplicating in-situ conditions when determining thermal conductivity for the deep crust.